1. Field of the Invention
This invention relates to room temperature vulcanizable organopolysiloxane compositions which are very useful as a masking material for electric or electronic parts which require dipping in a solder melt.
2. Description of the Prior Art
In the fabrication of printed boards used in various types of electric and electronic appliances, it is the common practice that capacitors, resistors and/or chip parts are connected to a printed board by an automatic soldering apparatus in order to increase the productivity. For this purpose, the printed board is dipped in a soldering bath maintained at a temperature of 250.degree. to 300.degree. C.
If the parts are very liable to deteriorate in quality when heat is applied, they cannot be dipped in a hot soldering bath as they are. Accordingly, these parts are usually masked with a protective material which can stand high temperatures, and are then immersed in a soldering bath. Subsequently, the masking material is removed. Organic rubber latices are frequently used as the masking material, with the attendant disadvantage that their heat resistance is unsatisfactory with poor releasability.
To overcome the above disadvantage, attempts have been made on room temperature vulcanizable or curable organopolysiloxane compositions because of their high heat resistance and good releasability, and some types of organopolysiloxane compositions have been in use. Although the known room temperature vulcanizable organopolysiloxane compositions have a high heat resistance, the cured film of the composition firmly adheres to a printed board after dipping in a soldering bath and becomes difficult to release. Accordingly, there is a demand for development of a masking material which undergoes little or no change in physical property when heated to 250.degree. to 300.degree. C. for several tens seconds and can be readily released from the board after the soldering.
We have made extensive studies on such a masking material or composition which is used to protect electric or electronic parts at the time of soldering, for example, on a printed board. As a result, it has been found that when a specific type of amide compound is added to known room temperature vulcanizable organopolysiloxane compositions for use as a masking material, this material can be readily released from the applied printed board after vulcanization at room temperature and dipping in a soldering bath.